A ray of light, after getting reflected twice from a hemispherical mirror of radius R, emerges parallel to the incident ray. The separation of the original incident ray and the final reflected ray is

1. R 2. R √2

3. 2R 4. R √3

The light incident and reflected will make angle of 90° each time. The tangent from both the reflected point meet and form 90° angle the perpendicular to tangent meet at centre and at centre the perpendiculars will form an angle of 90° . So the perpendiculars are radius and the distance can be calculated by pythagoras . From this the distance between incident and reflected light which are parallel to each other is R✓2